Otto told the California Department of Motor Vehicles and California Highway Patrol that its trucks “are not capable of operating in autonomous mode in California,” according to a DMV spokeswoman.
Now in the wake of a complaint filed by Consumer Watchdog, the DMV said it is looking into the issue. Consumer Watchdog provided a six-page report from Scott Ryvola, Otto software quality manager, that describes how test drivers on California roads press a dashboard button “to engage the self-driving system,” while remaining “extremely attentive and ready to take back full control whenever necessary.”

California’s self-driving regulations cover only those vehicles with a gross weight up to 10,000 pounds. Vehicles over that weight “shall not be approved for testing as autonomous vehicles on public roads,” the DMV rules say. Tractor cabs typically weigh 15,000 pounds or more, even without trailers. The DMV said it will work on regulations for self-driving commercial vehicles in the future.

As far as I know, the earliest use of the self-driving truck idea was in Miles J. Breuer's excellent 1932 story Technocracy:

The two fugitives jumped up and ran, knocking over several astonished people who were waiting for packages; their destination was an open door with daylight beyond. Out there was a row of trucks with laundry packages dropping into them from overhead chutes. They were automatic trucks such as are used for making deliveries beyond the pneumatic-tube zone.

They leaped into the foremost truck. Quentin set the switches on impulse for Bay Shore, because that was not where he wanted to go, and they both rolled back into the closed portion of the vehicle. The truck started slowly, gathered momentum, and automatically made its way out of the city.
(Read more about automatic trucks)